PS3-15. Comparison of Calculated and Measured Apparent Total Tract Calcium Digestibility in Pigs

Calcium (Ca) is an important driver of pig performance affecting negatively the phosphorus (P) utilization when in excess, but necessary for its deposition into bone. It is therefore important to be precise in feed formulation with this nutrient. Digestibility is the most precise method for many nutrients such as amino acids and phosphorus. New values of apparent and standardized digestibility of Ca are now available for most feed ingredients containing Ca. The objective of this work was to compare predicted values using new digestibility values of feed ingredients with measure apparent total tract digestibility of Ca in the literature. A database including all the information about apparent digestibility of Ca in pigs fed complete diet without phytase was built. A total of 53 publications and 153 diets were used. Apparent digestible Ca (% diet) measured was compared with calculated (% diet) using linear regression with SAS. No correction for study effect were made to test the capacity in varying conditions. The relative mean square prediction error (RMSPE) was calculated and divided into error of central tendency (ECT), regression (ER) and disturbance (ED). Factors that may affect this relationship were also tested. The results showed an intercept that differed from 0 with a value of 0.72% (P = 0.001) indicating that high digestible Ca values were more overestimated than low digestible Ca value for which regulations may have occurred. Then, a slope of 0.71 different from 1 (P < 0.001) indicates a systematic over-estimation of Ca digestibility. The RMSPE was 26% with 17, 13 and 70% of ECT, ER, ED respectively. Looking at the factors that may explain the overestimation, the pig physiological stage was found significant. The piglets’ category (body weight lower than 15 kg; n = 43) showed an intercept (0.21) and a slope (0.92) no longer significant with a RMSPE of 18.6% mostly from ED (92%). The model for other pig category (n = 112) showed an intercept of 0.90 and a slope of 0.64, a RMSPE of 28.9% with 25, 21 and 54% of ECT, ER, ED respectively. While the cause of this effect remains unclear and under investigation, further studies should focus on refining calcium digestibility estimates across pig growth stages to enhance predictive accuracy in feed formulation.